Buffer mechanism



Aug. 5, 1958 K. w. `MAIER BUFFER MECHANISM Filed April l2, 1957 INVENTOR.

KARL w. MAIER of concrete.

United States Patent O BUFFER MECHANISM Karl W. Maier, Cheshire, Conn., assgnor to Olin Mathie son Chemical Corporation, a corporation of Virginia Application April 12, 1957, Serial No. 652,506

Claims. (Cl. 123--7) This invention relates to buffer mechanisms and deals 1n particular with such mechanisms adapted to soften or cushion impacts of bodies moving at ultra high velocities,

such as pistons of powder-actuated or air-operated tools.

vof driving or shooting projectiles, such as nails, bolts,

studs, drill bits and other slugs or fasteners into a work piece, utilizing a piston propelled by compressed air or hot gases has been the selection and control of powder charges or air pressure, as the case may be, effective to drive the projectile into the work piece without damaging the tool or overdriving the fastener.

It is well known that the resistance offered to a given design of slug or fastener varies over wide ranges from work piece to work piece; the resistance varies, in fact, from area to area in a given work piece. For example, a projectile driven into concrete meets a resistance different from the value of resistance encountered in wood or a cinder block. Correspondingly, resistance to a projectile may vary from area to area within a given slab As a result of the wide range of resistances encountered, frequently the piston utilized to drive a fastener arrives at the end of its stroke with a very considerable portion of its energy unconsumed.

Frequently this unconsumed energy is dissipated by overdriving the fastener or by failure of the piston, both v'occurrences being highly undesirable.

Usually a stud is driven into a work piece to a certain predetermined depth with an allowed maximum or minimum depth dening a tolerance. By the term overdrive is meant driving a stud or other projectile beyond the tolerable distance.l

It is apparent that impacts occurring at velocities of 100 to 200 feet per second originate violent shock waves; the impact force being proportional to the impact velocity. In order to reduce impact forces, it is highly desirable to reduce the relative impact velocity of the impacting surfaces. In the present invention a reduction of impactv force is accomplished by bringing the impacting surfaces of the piston and the cylinder together along a fpair of mating tapered contours, after the fastener is set,

2,845,908 Patented Aug. 5,11958 ICC less than the longitudinal velocity and is proportional to the angle of taper.

In addition to variations in resistance occurring in different materials or in different area of a given material, the problem of over-driving a slug beyond tolerable limits stems from the fact that it is frequently necessary to have an exceedingly high powered stroke, initially, to start a fastener into the work and thereafter much less power is necessary to keep the projectile moving into the work,

The buffer device of the presentl invention is effective to cushion exceedingly fast moving pistons within a relatively short distance and is thereby effective to regulate accurately the depth to which a fastener is driven.

Accordingly, it is a particular object of the present invention to provide a novel buffer mechanism.

It is a further object of the invention to providel a buffer mechanism for powder-actuated or air-operated tools, or the like, effective to cushion the piston within a short interval of time and Within tolerable overdrive limits.

Another object ofthe invention is the provision of a piston-cylinder arrangement in the above general class of devices where one end of the cylinder wall is provided with a plurality of radially disposed slots to define a plurality of tines or prongs and reinforcing the exterior of the cylinder in the Vicinity of the tines with a Winding or serving of ends of Fiberglas filament or yarn suitably bonded with plastic to define a collet.

. A further object of the. present invention is the provision of a structure having the longitudinal strength or compressive resistance of a tube or cylinder While having radial resilience for bufferlng.

A buffer mechanism embodying certain features of the present invention maycomprise a tubular barrel member, a piston having a tapered contour disposed in the barrel and adapted to be driven along the longitudinal axis of the barrel in response to gas pressure, the forward end ofthe cylinder being formed with an internal tapered contour adapted to complement the tapered piston, the forward end of the cylinder wall being formed with a plurality of radially disposed grooves or slots for dividing the Wall into a plurality of tines, the interior tapered portion and the tines being so disposed that when the piston is advanced to bring the mating tapered portions into contact whereby the piston tends to spread the tines and a band of glass reinforced plastic disposed around the exterior of the tines effective to retain the tines against splitting.

Other features and advantages of the present invention will become apparent from the succeeding specification and drawings wherein:

Fig. l is a longitudinal sectional View of a buffer mechanism embracing the principles of the present invention. The section is defined by a plane passing through the longitudinal axis of the mechanism and cutting a pair of opposed tines.

Fig. 2 is an end view of the left end of the device shown in Fig. l. A

It is to be distinctly understood that although the exemplary embodiment of the invention shown and described herein illustrates the principles of the present invention as adapted to a powder actuated tool (wherein a powder charge is burned to advance a piston which, in turn, drives a projectile such as a nail or stud), it is entirely within the spirit and scope of the invention to .apply the principles thereof, namely, the scheme for buffering, to any piston tool no matter what its source of motivation or the character of the element upon which the vpiston performs work.

Referring now to the several figures there is shown in the illustrated embodiment of the invention a cylinder or barrel 1`0`having a bored plug 11 in threaded engagement '3 therewith for receiving a conventional cartridge 12. Disposed within the barrel and immediately ahead of the plug is a piston 13 having a base 14, a tapered neck 16 and a head 17. A compression chamber designatedby the reference numeral 15 is bounded by the plug 11 and the base of the piston. The piston is provided with a. suitable gas seal at the base and in theform of 'piston rings 18 and is adapted to move along the interior of the barrel in the direction shown by .the arrowuntilfthetaperedneck 16 encounters a mating tapered portion 19 formed on the interior of the barrel.

In customary manner, a.- suitable proiectile,`such 1 as the stud 21 disposed in the boreof .the bar-relis driven into a work piece when theihead 117f strikesi'the' stud.

The forward portion ofiithe barrel or the left vrend,as viewed lin Fig. 1,.. is formedwith'aplurality of slots 22 so as to divide .the barrel intola plurality of prongs or tines 23. For.. convenience, thisfportion of the barrel may -be referred to hereinafter las 1a chuckl vor collet.

The chuck endof the Vbarrel is undercut to receive a winding or serving of strands or -iilaments of Fiberglas wrapped about the undercut-portion and-suitably impregnated with a plastic binder so as to form a composite band there around as indicated generally by the reference numeral 24. It is important that the strands `or laments of'Fiberglas wound or servedaround the exterior of the collet be so arranged that a bursting load tending to swell the tines or prongs outwardly willplacethe Fiberglas under a hoop stress or a tensile stress. By so disposing the ends of Fiberglas, it is possible to take advantage of the maximum tensile strength available Yin Fiberglas reinforced Yplastics which, as is'well known, is in excess of 200,000 lbs. per square inch.

Frequently it may be desirable to provide a loose shim or liner of relatively light gaugemetal between the band of Fiberglas reinforced plastic andthe exterior of v'the tines, as at 20, to avoid undue friction or Wear between the interfaces of the tines and the band.

The operation of the tool is as follows:

Assume that a projectile such as the projectile 21 has been disposed within the barrel 10 and'that the'piston 13 is retracted to the position shown in Fig. l.

Firing of the cartridge 12 by well known means will generate hot gases in the chamber 1 5 which rapidly expand to drive the piston to the left, las viewed in Fig. l, whereupon thehead 17 engages and moves the stud 21 out of the barrel anddrives it into a workpiece.

In tools of this nature, it isdesirable, as stated previously, to decelerate-or stop the piston as soon as possible after it has driven its projectile and within the very short additional length of stroke allowed for overdrive.

Accordingly, the tapered neck 16 and the mating tapered portion 19 of the barrel are sodisposed that upon a given length of stroke of thepiston the corresponding tapered portions engage one kanother to load the collet tending to move the tines outwardly in turn loading .the band 24.

Since the structural element of the band 24 is Fiberglas having a very high tensile/strength and a considerable elongation (more than 2%) a high energy .is readily absorbed by the band in swelling without exceeding the elastic limits of theFiberglas.

It is frequently desirable-to form the tapered portion 19 on the barrel such that the included angle, alpha, represented by the dotted lines is-slightly greater than the corresponding angle, beta, formed on the neck of the piston. In this way there .is a; gradual loading of the reinforcing band 24 wherein the mating tapered portions rst make line contact with oneanother :and .thereafter fit snugly.

inherently, the tapered formation or contour ofthe piston` and .the .-cylinder Vhave .the .following advantages:

(a) lConcentration of stresses 4on the piston areavoided.

(b) There .is a transfer of longitudinal motion .0f the piston into radial motion of the tines and into hoop stress in the Fiberglas.

(c) There is a reduction in velocity of impact between the impacting surfaces of the piston and cylinder and a corresponding reduction of surface stress.

(d) The surface of impact is increased.

(e) There is a maintenance .of longitudinal stiifness of the barrel while using radial resilience of the tines for buffering.

(f) Self-releasing tapers (tapers whose included angles are large .enough to avoid frictional seizingnpon impact) may be selected effective to reduce thevelocity of impacting surfaces offpistontand -cylinder from 200 feet per second to as low as 50 feet per second.

It is anticipated that various arrangements and modiiications of the present invention may be devised wherein: (l) a wide variety of plastic binders may beutilized to reduce the winding of Fiberglas to .acompositemass (2) the density'of the Fiberglas within the vcomposite mass may be varied by varying, forexample, the tension with which vthe glass filaments are wound `(3) .the design of the mating tapered portionsmay be adjusted to include different tapers or contours. Nevertheless alllthese modiiications are entirely within thespiritand yscope-ofthe present invention.

What is claimed is:

l. A buffer mechanism for cushioning the impactof a piston colliding atan ultra high velocitycomprising a tubular memberfor slidably. receiving .the-piston,imeans for applying uid pressure .to the piston to. drivethe piston, one end of said tubularmember being formed with a plurality oftines, the.internal surfacegof saidtubular member being formed .in the vicinity of Asaid tineswith a tapered contour adapted to mate with I a.corresponding tapered contour formedon the'ipistomdsaidpiston being eective to spread the tines when'the piston is driven in a direction which tendsto bring .the taperedportions into engagement, and a winding Vof glass reinforced plastic disposed about the exterior ofthe tines effective toresist the tendency for the tines .to spread.

2. A buffer mechanism forcushioning thetimpact of a piston colliding at an .ultra high velocity comprising-an apertured member for slidably receiving y,theltpistom a compression chamber within the member for applying fluid pressure to the base-of the piston to'drivethe piston,

-one end of said member being formedwith aplurality of tines, thenternal surface of the piston being formed with a tapered contour adapted-,to .mate with'a correspondingtapered. contour formed onthe pistonand effective to spread the tines when thepiston is .drivenlin a direction which tends to bring the tapered portions into engagement and aband offglass reinforced plastic disposed aboutthe exterior of the tines eiective to resistthe tendencyfor Ythe tines to kspread whereby the `piston is brought to a cushionedstop.

3. A buffer mechanism for cushioning the impactof a piston colliding at -ultra ,high velocity comprising a tubular member forslidably receivingthe piston, a compression chamber within the tubular member for applying fluid pressure to the head of `the piston, one. endof said tubularmember. being formed rwith afplurality-of tines, the internal contour of the tubular member being formed with a tapered portion adaptedto mate Awith a corresponding .taperedportion formed onthefpiston and effective to spread the tines when thel piston .is driven in a direction which tends to bring theetapered, portions into engagement, a band of glass reinforced plastic. disposed about the exterior ofthe tines eiectiveito resist the tendency for the tines to spread ,whereby the-,piston-:is brought to a cushioned stopi anda -shimfdisposed'fbetween the interfaces `of the tines. andthe: glass reinforced band to protect the inner diameterA of the' band.

4. A buierrnechanism.adapted-to cushion. .theimpact between a piston moving at an ultra high velocity u'pon collision with a piston cylinder wall comprising a cylinder having a compression chamber at one end thereof and a tapering internal contour at the other end thereof, the walls of said cylinder being formed with a plurality of radially disposed slots in the vicinity of said tapered portion and a composite band of glass reinforced plastic disposed about said cylinder in the area of said slots eifective to retain the slotted end of the cylinder against a bursting load.

5. A buffer mechanism adapted to cushion the impact between a piston moving at an ultra high velocity upon 6 collision with a piston cylinder wall comprising a cylinder having a compression chamber at one end thereof and an internal tapered portion generally defining a frustum of a cone in cross section at the other end thereof, the walls of said cylinder being formed with a plurality of radially disposed slots in the vicinity of said tapered portion and a composite band of glass reinforced plastic disposed about said cylinder in the area of said slots effective to retain the forward end of the cylinder against bursting, said glass taking the form of a circumferential winding of filaments.

No references cited. 

